Digital reprographic machines have traditionally been designed using eight bits for the image data. As print quality requirements for the output of these reprographic machines have grown, especially for color reprographics, a variety of methods have been used to increase the quality; however the image path bit width has remained constant.
Newer technologies use image data paths with more than eight bits. However, it would be desirable to be able to transmit and process the data from the wider bit image data paths on older, legacy, machines.
One conventional approach used N-bit to 8-bit error diffusion to get the effect of more than eight bits. While such a technique produced some increase in image quality, it also increased the graininess of the error diffused image.
For many of the older 8-bit data path machines, the image data path included a tag bit path in parallel with the image data path. The tag bit path was used to convey extra information about the corresponding image data word that could be used to chose between alternate processing methods along the image path. For example, the tag bit word could be used to choose between one of several different halftoning schemes. The tag bits and the image bits are separate streams conveying different information.
While the design of the machines using a tag bit path does not allow using the tag bits to directly contain image data, it would be useful to be able to use the tag bits to expand the effective number of bits to allow the legacy machines to accept data from a newer N-bit image source, where N is greater than the original eight bits that the image path was designed for.